DISTRIBUTION OF C¹⁴-SUCROSE AND I¹²⁵-IODIDE IN THE CENTRAL NERVOUS SYSTEM OF THE CAT AFTER VARIOUS ROUTES OF INJECTION INTO THE CEREBROSPINAL FLUID

¹ Children's Hospital Medical Center and Departments of Neurology and Pharmacology, Harvard Medical School, Boston, Massachusetts

The purpose of this study was to determine which method of drug administration into the cerebrospinal fluid would provide the most effective penetration and distribution in the central nervous system. C¹⁴-sucrose and I¹²⁵-iodide were chosen to represent solutes with limited access to the brain and cerebrospinal fluid after systemic administration. Isotope was administered to cats by single lumbar, cisternal or ventricular injections, or by continuous ventricular infusion, in fractional volumes comparable to those used in man. The effects of anesthesia and the time course of isotope penetration and retention were studied. Samples were obtained for radio-assay from three regions of the cerebrospinal fluid, plasma and nine regions of the brain and spinal cord. Comparable concentrations of C¹⁴ and I¹²⁵ were found in the brain 5 min after injection. Thereafter, I¹²⁵ was cleared from tissue more rapidly than C¹⁴. The concentration of either isotope in the cortex was proportional to the concentration in the adjacent cerebrospinal fluid. It was found that the most uniform distribution and generally greatest concentration of isotope in the central nervous system resulted from a single intraventricular injection in anesthetized animals.